tea science october 2016
EDITOR'S NOTE
Hello fellow tea lovers, Welcome to my first ever tea science issue. Shout out to Adam S. for the suggestion! This issue ran a bit later than usual but I'm excited to articles from some of my favorite people in the tea world. The world of tea is incredibly diverse and you can get REALLY nerdy about it in a million different ways. The articles featured here are usually from tea companies but submissions are welcome whether you are a tea seller, blogger or just an enthusiast. My main goal is further tea education and to give back to the tea community that has given so much to me. As always, I'd love to hear your questions, thoughts, feedback and ideas. What would you like to see in the next issues? Please feel free to shoot me an email at nicole@teaformeplease.com. My inbox is always open! Nicole
CHEMICAL COMPOUNDS IN TEA BY TONY GEBELY
Caffeine
Tea chemistry is complex. Just how complex? Well, on the bush, tea leaves contain thousands of chemical compounds, when they are processed, these compounds break down, form complexes and form new compounds. When we steep tea leaves, our senses are tingled by the thousands of volatile compounds ( collectively known as the “ aroma complex ”) from the tea liquor and the thousands of non-volatile compounds and the complexes between them, not all of which are water soluble, and the ones that are water soluble are soluble at a function of the properties of the water used for steeping like temperature, total dissolved solids, pH, etc. So all of this makes it very difficult to generalize and say that x chemical is responsible for y taste. Many tea chemicals have been categorized into broad groups, and collectively we have some idea of what happens to these groups during processing and what flavors and aromas they are responsible for. As tea gains popularity, there is no doubt that more research will be done on tea chemistry and we’ll have a clearer picture of what is going on chemically from the field to the cup.
Plant leaves are made up of mostly water, when they are removed from the plant they begin to wilt and lose water. Tea leaves are no exception to this. In the field, they are made up of mostly water, when they are plucked the leaves begin to lose water or wilt, a process called withering in the tea industry. As tea leaves wither, their cell walls begin to break down and the chemical components inside come in contact with oxygen and each another, spurring on a group of reactions we call oxidation. Over the years, tea producers have learned to control the natural tendency of tea leaves to wither and oxidize in order to produce a finished tea that has a desirable appearance, aroma, flavor, and taste using methods we’ll refer to as tea processing. Amazingly, for hundreds of years tea makers have produced drinkable teas using principles of withering and oxidation with no knowledge of the underlying chemistry. From what we know today, the most important compounds in fresh tea leaves responsible for producing teas with desirable appearance, aroma, flavor, and taste are: polyphenols, amino acids, enzymes, pigments, carbohydrates, methylxanthines, minerals and many volatile flavor and aromatic compounds. These components undergo changes during tea processing to produce what we’ll call a ‘finished’ or ‘made’ tea – one that has been processed and is ready for packaging or steeping. Let’s take a look at each of these compounds beginning with the most abundant, polyphenols.
Polyphenols In steeped tea, polyphenols are largely responsible for astringency. The term polyphenol simply refers to a categorization of compounds composed of many phenolic groups, hence the name poly-phenol. These compounds are plant metabolites produced as a defense against insects and other animals and are the most abundant compounds in tea comprising as much as 30-40% of both freshly plucked tea leaves and solids in tea liquor 1. They are derived from amino acids via sunlight and therefore tea grown in the shade has a smaller concentration of polyphenols and a higher concentration of amino acids 2. The bud and first leaf have the highest concentration of polyphenols and polyphenol levels decrease in each leaf moving down the plant 3.
4 There are an estimated 30,000 polyphenolic compounds in tea , flavonoids are arguably the most important group of polyphenols in tea and are the source of the many health claims surrounding tea, and specifically tea antioxidants. Within the flavonoid group, flavanols (also known as flavan-3-ols) are the most prevalent. Flavanols are also referred to as tannins, and during oxidation are converted to theaflavins and thearubigins—the compounds responsible for the dark color and robust flavors notably present in black teas. The major flavanols in tea are: catechin (C), epicatechin (EC), epicatechin gallate (ECG), gallocatechin (GC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). EGCG is the most active of these catechins and is often the subject of studies regarding tea antioxidants. Tea flavanols are sometimes collectively referred to as catechins. Besides flavanols, tea flavonoids also include flavonols, flavones, isoflavones, and anthocyanins; all of which contribute to the color of a tea’s infusion and its taste.
Amino Acids Amino acids give tea its brothiness, or umami taste. Tea leaves contain many amino acids, the most abundant of which is theanine. Camellia sinensis, a mushroom called Boletus badius, and an plant called guayusa (which is often processed made into a tisane) are the only three natural sources of theanine found thus far in nature. In the tea field, sunlight converts amino acids to polyphenols, and as such; shade grown tea contains more amino acids than tea grown in direct sunlight. Some tea bushes are even deliberately shaded for several weeks before harvest to enhance the tea’s amino acid content. Theanine, more specifically L-Theanine is responsible for promoting alpha brain wave activity which promotes relaxation. L-Theanine in concert with caffeine can induce a state of “mindful alterness”1in the tea drinker. In steeped tea, amino acids make up 6% of the extract solids . Enzymes Polyphenol oxidase and peroxidase are the most important enzymes in tea leaves. They are responsible for the enzymatic browning of tea leaves that takes place when the cell walls in the leaves are broken and the polyphenols are exposed to oxygen – otherwise known as oxidation.
These enzymes may be denatured or deactivated using heat so that browning cannot occur; this is one of the first steps in green tea production and is why finished green tea leaves remain green. The enzymes may also be denatured by simply depriving them of moisture for a time which is what happens during the long withering period in white tea production.
Pigments Plant pigments are responsible for absorbing light for photosynthesis. Pigments also give leaves their color. There are two major groups of pigments in fresh tea leaves: chlorophylls and carotenoids. These pigments condense during withering and oxidation and become darker. During oxidation, the green color of tea chlorophylls is converted to black pigments known as pheophytins. This conversion leads to the dark appearance of finished oxidized teas. Tea carotenoids are another pigment group found in tea leaves and are mainly composed of carotenes which are orange and xanthophylls which are yellow and are also responsible for the color of finished tea leaves. Carbohydrates All plants store energy formed during photosynthesis in starches and sugars, otherwise known as carbohydrates. Plants later use this stored energy to fuel important reactions, in tea, carbohydrates help to fuel the enzymatic reactions that take place during oxidation and are also responsible for the creation of polyphenols 1 in young tea leaves. Carbohydrates make up on average 11% of extract solids in steeped tea and lend to its sweetness. Methylxanthines Methylxanthines in tea include the stimulant caffeine and two similar compounds: theobromine and theophylline. The tea plant creates these chemicals as a natural combatant towards insects and other animals. On average, methylxanthines in tea leaves5make up 2% to 5% of the dry weight of the fresh leaves . Methylxanthines also contribute to a bitter taste in the tea infusion. Levels of these compounds depend on the variety and cultivar of Camellia sinensis used, climate, age of the leaves, and the propagation method (seed vs. cutting) used on the plant.
Minerals 5 28 mineral elements have been found in the tea flush . Compared to other plants, tea has a higher than average amount of: fluorine, manganese, arsenic, nickel, selenium, 5 iodine, aluminum, and potassium . Tea also has an unusually high amount of fluorine, which has been known to help prevent tooth decay in humans, however too much fluorine can be harmful. It is important to note that fluorine occurs in greater amounts in older tea leaves. Tea minerals vary greatly with each harvest and change greatly during processing.
Crystal Structure of Flourine
Volatiles 6 The volatile substances in tea leaves are largely responsible for a tea’s flavor and aroma. The aroma complex of tea is made up of hundreds (maybe even thousands) of flavor and aroma compounds that exist in trace amounts. Many of these aromatic compounds do not exist in fresh tea leaves and are derived from other substances during processing. The flavor and aroma of each tea depends on a wide variety of combinations of these compounds, hence the name aroma complex. Compounds such as, linalool and linalool oxide are responsible for sweetness; geraniol and phenylacetaldehyde are responsible for floral aromas; nerolidol, benzaldehyde, methyl salicylate, and phenyl ethanol are responsible for fruity flavors; and trans-2-hexenal, nhexanal, cis-3-hexenol, and b-ionone are responsible for a tea’s fresh flavor . When studying tea’s aroma complex, it is sometimes broken into two parts: primary aroma (from fresh tea leaves) and secondary aroma (products of manufacture). Regardless, more and more research is being done on tea volatiles and how our olfaction system works in general, so we may expect some clarity on this issue in the coming years.
Excerpt from Tea: A User's Guide published here with permission from the author. Tony Gebely is a thought leader in the American tea industry and a lifelong student of tea. He has worked in all aspects of the tea industry including sourcing, blending, business strategy and marketing. He is also the creator of World of Tea, an awardwinning tea education and news site.
Get your copy of Tea: A User's Guide here!
Sources: 1. Harbowy, Matthew E., and Douglas A. Balentine. “Tea Chemistry.” Critical Reviews in Plant Sciences 16, no. 5 1997: 415–480 2. Ercisli, Sezai, Emine Orhan, Ozlem Ozdemir, Memnune Sengul, and Neva Gungor. “Seasonal Variation of Total Phenolic, Antioxidant Activity, Plant Nutritional Elements, and Fatty Acids in Tea Leaves Grown in Turkey.” Pharmaceutical Biology 46 (2008): 683–687 3. Bhatia, I.S. “Composition of Leaf in Relation to Liquor Characteristics of Made Tea.” Two and a Bud 83 (1961): 11–14. 4. Uncovering the secrets of tea – http://www.rsc.org/chemistryworld/2012/11/teahealth-benefits 5. Zhen, Yong-su. Tea: Bioactivity and Therapeutic Potential. London: Taylor & Francis, 2002 6. “Tea Chemistry – Tocklai”. Tocklai Tea Research Association, n.d. http://www.tocklai.org/activities/tea-chemistry/
Revisiting Medications and Green Tea C. Novitzke, PhD Every year we see sensationalist news headlines like “Man Dies from Green Tea,” or “Green Tea Proves Fatal.” Most of us who are tea drinkers cringe at articles like these designed to scare consumers and attract hits on news websites. What kind of evidence supports these articles? As an older person taking medications for blood pressure and who also enjoys a great deal of green tea, this author decided to investigate the socalled evidence and found a wealth of shoddy journalism and weak studies. The Case of the 44 Year Old Man on Warfarin This single case from 1999 of a man taking Warfarin, aka Coumadin, an older but still somewhat common blood thinner, has resulted in more articles citing the “fatal dangers” of green tea more than any other case. “CASE SUMMARY: A 44yearold white man was receiving warfarin for thromboembolic prophylaxis secondary to a St. Jude mechanical valve replacement in the aortic position. The patient had an international normalized ratio (INR) of 3.20 approximately one month prior to entering our clinic, and an INR of 3.79 on entering our clinic. Twentytwo days later his INR was 1.37. One month later the patient's INR was 1.14. It was subsequently discovered that the patient began drinking onehalf to one gallon of green tea per day about one week prior to the INR of 1.37. On discontinuation of the green tea, 1 the patient's INR increased to 2.55 (Taylor & Wilt, 1999).”
This single case is cited by the US National Institute of Health Publication D273 “Green Tea” in a warning about green tea. This single case study is also cited by the Cleveland Medical Centers 2 and even migrated to New Zealand’s University of Auckland Health and Medical Sciences where it 3 appears in a patient sheet for “Men on Warfarin,” which points to Vitamin K in tea as the interaction factor with Warfarin. Green tea contains small amounts of Vitamin K also present in foods like kale and broccoli. The NIH, Cleveland Medical Centers, and the University of Auckland are all considered “safe” and reliable medical information sources. Yet all three are using a single case study and generalizing it to everyone on any medication no matter how much tea they drink. Also notable is that the man suddenly starting drinking green tea only after starting Warfarin, and had no prior tolerance. One man, who is the only reported case like this so far, has led to more articles on the dangers of green tea and medications in general than any other source. Green Tea Supplements Let us look once more at the above NIH publication D273 “Green Tea.” It not only cites the Case of the Warfarin Man, but also has one other interesting citation that is supposed to point to warnings about Green Tea. The citation is a metastudy of 216 “problem” cases from 19662008 on green tea extracts (pills, dietary supplements) as causing no significant issues. Based on this safety review, the DSI EC determined that when dietary supplement products containing green tea extracts are used and formulated appropriately the Committee is unaware of significant safety issues that would prohibit monograph development, provided a caution statement is included in the labelling [sic] section (Sarma et. al., 2008).” [emphasis mine] So, the NIH publication D273 on Green Tea is actually using an article as “evidence” for caution which in fact shows the opposite! The cited article is a metaanalysis (good study review) of over forty years of cases of possible problems by green tea supplements and found no issues at all. What is the US government NIH thinking? If we need a cautionary statement on green tea because of Warfarin Man, then surely we need one on bunches of kale as well." Blood Pressure Medication Another headline appeared two years ago in the International Business Times “Green tea combined 4 with medications proves fatal (Mahesh, 2014).” This journalistic piece cites the Daily Mail newspaper and Health News, hardly credible sources. But the study which spurred the “fatal” 5 headlines is actually a Japan study with the blood pressure medication Nadolol.
This study used 10 healthy volunteers and had them drink either 700 milliliters of water or green tea per day for two weeks, and then take 30 mg dose of Nadolol with either three cups of green tea or water on top of their nearly liter a day liquid. IBT and the Daily Mail reported “76%” reduction in the drug in the blood of the subjects, an error. The study actually found “plasma reductions of nadolol by 85.3% [tea people] and 85.0% [water people]. Did not alter systolic blood pressure or renal clearance (Ibid, 432).” We have 10 healthy people, hardly enough for a large study, drinking either a large amount of water or tea per day. Scientifically the difference is 0.3% between the water people and tea people. The only tentative conclusion on healthy people is that any type liquid is likely to flush out a drug from blood plasma, and no conclusion about people with high blood pressure. This is FAR cry from the IBT headline of “Green Tea Combined with Medications Proves Fatal.” Nobody died, and green tea effectively did little more than water. Statistical significance is not the same thing as an effect difference. Anybody drinking this much liquid is going to have only 15% of the medication appearing in plasma, not to mention that many people normally drink 2/3 of a liter of liquid per day. Back to Reality Small studies and single cases lead to sensational headlines. This author looked at popular journalism articles and found links to studies that did not scientifically support the headlines. The truth is that research linking green tea with medication interactions is weak. The truth is governments and health care entities are giving advice based on single cases. On the other hand, a conservative opinion is certainly warranted when a patient is taking medications. Bottom line, if you are taking medications, then talk with your doctor who is most likely to give you that conservative opinion. Know that opinion is based on very little evidence and is simply meant to prevent harm. But green tea is probably not going to kill you.
Carie Novitzke, PhD is the author of Cwyn’s Death by Tea blog. Trying to die by green tea as quickly as possible, the author has not thus far succeeded.
References 1. National Health Institute, 2012. NCCIH Publication No.: D273. Green Tea. Created: May 2005, Updated: April 2012. https://www.ncbi.nlm.nih.gov/pubmed/10332534 2. Leonard, M. (2001). Interactions between herbs and cardiac medications. Clevelend Clinical Medication Publications Updates. Mar/Apr 4:2, website. http://www.clevelandclinicmeded.com/medicalpubs/pharmacy/MarApr2001/herbs_cardiac.htm 3. University of Auckland Health and Medical Sciences (no date). Information sheet 17: for men on Warfarin. Patient brochure as online PDF. https://www.fmhs.auckland.ac.nz/assets/fmhs/sms/nutrition/pcd/docs/is17formenonwarfarin.pdf 4. Mahesh, M. (2014). Green tea combined with medications proves fatal, popular beverage lowers effects of blood pressure drugs. International Business Times. 15 Jan 2014. http://www.ibtimes.co.in/greenteacombinedwithmedicationsprovesfatalpopularbeverage lowerseffectsofbloodpressuredrugs534483 IBT January 2014 5.Misaka, S., Yatabe, J., Müller, F., Takano, K., Kawabe, K., Glaeser, H., Yatabe, M., Onoue, S., Werba, J., Watanabe, H., Yamada, S., Fromm, M. & Kimura, J. (2014). Green Tea Ingestion Greatly Reduces Plasma Concentrations of Nadolol in Healthy Subjects. Clinical Pharmacology & Therapeutics, 95: 432–438. doi:10.1038/clpt.2013.241 http://onlinelibrary.wiley.com/doi/10.1038/clpt.2013.241/full.
VARIETIES, CULTIVARS, CLONES–O H, MY! By Michael J. Coffey
Before we get into the details, let’s get warmed up with what we mean by “the tea plant.” That would be Camellia sinensis. As you may remember from your first biology class in school, the Latin name of plants and animals are made of two (bi) names (nomen) in a system known as binomial nomenclature. The first name is the larger category: the genus. The second is a subdivision of the genus: the species. Therefore, the tea plant is in the genus Camellia, and is more specifically the Chinese species (since “sinensis” refers to things Chinese). As you may also remember from biology class, there are larger categories like “phyllum” and “family” and so forth, but we can ignore those for the purposes of this article. We’re interested in the smaller ones. The next smaller category is the variety. NOMADIC
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In botany, varieties are all members of a species that have some physical characteristics that distinguish them from one another, but that aren’t so different that they’d be considered a different species. In dogs, we might call this a “breed” and in humans we might call it “race” but the basic concept is the same with plants—still the same species, but with differentiating physical characteristics, and ones that typically developed in different geographic regions. Different botanical classification systems deal with the tea plant differently. Most often in the tea industry, though, we see two varieties mentioned: sinensis and assamica. But it’s not really that simple. As mentioned in Tea: Cultivation to consumption (K.C. Willson & M.N. Clifford, 1992), “Tea is a heterogenous plant with many overlapping morphological, biochemical and physiological attributes.” In other words, there is some discussion about whether there are more or fewer botanical varieties than this and how that variation should be classified. Some suggest that Camellia sinensis var. sinensis and Camellia sinensis var. assamica were always, or have become, so interbred that they simply represent extremes of the natural variation in Camellia sinensis and therefore have no distinct varieties. Others suggest different breakdowns based on different features. In these other proposed classifications, you might see at the variety level: “lasiocalyx,” “irrawadiensis,” “Cambodiensis,” “sasanqua,” “bohea,” “parviflora” or “macrophylla.” Some even take the variety name and use it as the species, as in Camellia assamica. All that said, the most common scientific or botanical way of classifying the tea plant is Genus: Camellia Species: sinensis Variety: sinensis or assamica
Now we come to the word “varietal,” which Tony Gebely addressed recently on his blog . It basically boils down to simple grammar. “Variety” is a noun, and “varietal” is an adjective. Therefore, if someone says that a certain tea is “made from a varietal developed in…” they’re making the same grammatical error as if you said, “This is my book of grammatical” rather than “book of grammar.” Note that the ending al is the same in both cases, as that’s a common adjectival (there it is again!) ending. Correct usage of these terms would be something like, “This tea was made from a variety developed in…” and “Its varietal characteristics include…” Another quick summary then: Variety (n.) a particular type of plant Varietal (adj.) of or about a variety Now there’s two last things to cover: cultivar and clone/clonal (yes, it’s the same grammar—noun and adjective). For this, we need to talk about sex a little. As you probably know, sexual reproduction results in offspring that often take on characteristics of both parents. For the tea plant, sex consists of pollinators taking pollen from one plant and applying it to the flowers of another plant. In nature, that’s often done by insects, but with plants used in human agriculture, it can be humans that, well, perform this crucial sexual act for the plants. When tea plants have sex, their offspring are the plants that grow from the seeds that get produced. Tea plants, though, have a really wide range of variability when they make seeds. The same pair of plants could produce seeds that seem like they were maybe the milkman’s kids—extremely different from the parents. This variability makes it difficult for farmers to produce a consistent agricultural product. If things like yield, drought tolerance, pest susceptibility, quality, and so forth are hugely different from plant to plant throughout the field, it makes the farmer’s life much harder. With this type of plant, when used in agriculture, asexual reproduction methods are often used. Techniques such as cuttings, grafts, and division are common ways of making more plants without the use of seeds. They also all produce “children” that are genetically identical to the “parent.” I put those terms in quotes because although the tea industry likes to talk about the “mother plant” and so forth, they are in a very real sense simply multiple copies of the same plant. The technical term for this is a clone. It’s basically making identical twins, reliably, over and over again. A clonal variety, then, isn’t the same as the “variety” above—it’s simply referring to the whole group of genetically identical plants kept pure by vegetative propagation. If you really want to get deep into tea agriculture, you get to start learning the secret code numbers for distinct clones such as BB35, TRI/68, and TV17, for example, each known for a specific set of characteristics that a farmer could chose based on his or her needs. And this brings us to the word “cultivar.” The word is usually described as being a portmanteau of “cultivated variety” although if you want to go deeper down that rabbithole, the first part might also come from “cultigen” which I won’t talk more about for sanity’s sake. Cultivars are essentially the plants that have been selected by humans to cultivate. Although there’s a registry for plant cultivars, it’s not really tied to particular biological/botanical nomenclature. It’s tied to how humans use it.
When new cultivars are developed, it’s usually through sexual reproduction. Botanists take plants with some qualities they like, breed them, and see what qualities the genetic lottery gives the kids. When they find an offspring plant that’s different and useful enough, they make cuttings for several “generations” to make sure no weird variations that they don’t want will pop up. Once that has been determined, they usually then only propagate the plant asexually so as to maintain the new clonal features. However, if a particular group of plants seem to be able to maintain the desired characteristics through seed, a sexually propagated cultivar can exist, too. It’s just less common with the tea plant in particular because of that tendency of producing lots of very different plants when seed is used. Not so difficult…except that always more complicated than you think. There’s a slight wrinkle in that not everyone in the full breadth of the tea industry use the words in the same way. While “variety” the way I described it above is true from a scientific/botanical standpoint, that’s not how the word is typically used in the industry, since most of the people in the industry aren’t scientists. If you take out both the scientists and the farmers, most of the rest of the people use the word “variety” to refer to the cultivar (as described above). So you hear tea “experts” and tea shop owners talk about the variety (or, if they make the grammatical error, the varietal) that a particular tea is made from. Then comes the farmers. The group of humanselectedforagriculture plants which the scientists are calling a cultivar and industry folks are calling variety has yet another word that’s used by English speaking tea growers: Jat. This is a term that comes from India (where the first Englishspeaking tea growers did their thing) and means, as far as I can discern, something akin to “tribe.” So we might give that a summary as cultivar (botany) = jat (producers) = variety (general industry). So there you go. Aren’t you glad you asked? TL;DR — Variety is a subcategory of species; varietal is the adjective form of variety. A tea clone is a type of plant that has been propagated through cuttings. A cultivar is a ‘cultivated variety’ and in theory could be either a clone, or a plants produced through seed, but is a term used from a humanuse standpoint, not a biological one. Though they are properly called cultivars, many tea producers use the word jat, and the general industry calls them varieties (a different meaning from the species subcategory that started this paragraph). Varieties, Cultivars, Clonesoh, my originally appeared on Teageek.net on June 25th, 2013 and reprinted here with permission by the author.
Michael J. Coffey is an educator with sociallyunacceptable levels of tea knowledge as well as the founder of Tea Geek.
Oxidation vs Fermentation THE GREAT TEA DEBATE BY NICOLE MARTIN
When I first started drinking tea everyone referred to the changes that occur in tea during
processing as fermentation. It has become a bit of a raging debate as to whether oxidation is
accurate. Since this is my first science themed journal, I thought it would be a good time to tackle
this issue. Now, what exactly do these terms mean?
Fermentation is a metabolic process where sugar is converted into acids, gasses, and alcohol. It
usually carried out by an agent such as bacteria and yeast. Fermentation can occur naturally but
humans learned long ago how to manipulate this process in order to make alcoholic beverages like
beer and wine. Unless we are referring to kombucha, fermentation is not what is occurring during the
manufacture of most tea.
Oxidation is an enzymatic process that as the name implies, requires oxygen. This is similar to what
happens to the way an apple slice turns brown when it is exposed to air. Polyphenols in the leaves
absorb oxygen, converting them to polyphenol oxidase (PPO). PPO is responsible for the creation of
thearubigins. This substance gives black tea leaves their reddish color as well adds depth of flavor.
Applying heat to the leaves halts the process of oxidation.
Browning apple slices is a similar process to what happens to tea leaves when they oxidize
I was working for a French tea company and tried to explain to them that fermentation is not exactly
accurate. My superiors replied that in France, oxidation is considered a chemical process while
fermentation is considered a biological process. I suppose this makes sense when we consider that
iron rusting is also a type of oxidation. They believed that this cultural bias would affect whether or
not consumers believed their product to be natural. Perhaps this is part of the reason why there is
still so much confusion in the tea world. I believe there are also issues with translating Chinese
terms to English that may have played a part.
Puerh is one of the few exceptions to this rule. Shou, or cooked puerh, is inoculated with bacteria to
initiate fermentation. The process is similar to the way that mulch is created. There is some debate
about whether sheng, also known as raw puerh, is truly fermented. Some categorize it as a green tea
for this reason. However, there is some bacteria action involved when a tea is aged, particularly in
humid storage.
This is a very simplified explanation of a complex topic. An entire book could be written on it but
hopefully this will help to clear some things up. It is my hope that the industry will eventually come to
a consensus about using oxidation rather than fermentation. It’s important for educational purposes
both for those in the biz and for consumers, particularly in the United States where we are already so
behind the rest of the tea drinking world.